Charged particle beam devices can be used, for example, in electron beam inspection (EBI), defect review and critical dimension measurement. Upon irradiation of a specimen or sample by a primary charged particle beam, signal charged particles, such as secondary electrons (SE) or backscattered charged particles, are created, which may carry information about the topography of the sample, the chemical constituents of the sample, the electrostatic potential of the sample and other information about the sample. The signal charged particles are collected and guided to a sensor, e.g., a scintillator, a pin diode or the like.
The performance of a charged particle source, such as an electron emitter, providing the primary charged particle beam in a charged particle beam device is of particular interest. As an example, high brightness charged particle sources and/or high emission current sources with high emission stability are beneficial. The charged particle sources are operated under vacuum conditions, wherein the performance of the charged particle sources can be related to a quality of the vacuum.
Thermal Field Emitter (TFE) are established as electron sources for electron microscopes, especially due to the relatively high brightness, relatively small energy width, moderate vacuum standards and good short term emission stability and low beam current noise. However, commercially available TFE often exhibit unwanted stability problems, such as a long term, continuous decrease in angular intensity, which is attributed to a general growth of the tip, which leads to a reduction of field strength at the tip apex, hence reduced emission current and spontaneous changes in angular intensity (brightness). The general growth of the tip, the reduction of the field strength, and the reduced emission current are known as so-called ring collapsing, which is usually attributed to the re-arranging of atoms in the atom layers at the tip of the emitter, where the electrons are released.
In view of the above, it is an aim to provide an emitter for a charged particle beam, a charged particle beam device, and a method for producing and operating an emitter for a charged particle beam device that overcome at least some of the problems in the art.